Planar optical waveguides can be formed in polymers by using a core polymer and a cladding polymer with the core polymer refractive index slightly higher than that of the cladding polymer across the near infrared region of the optical telecommunication window from approximately 1200 to 1700 nanometers. A general approach to making such polymer optical waveguides is to dispose an undercladding polymer film layer on a silicon substrate and then a polymer core layer on top of the undercladding layer. The polymer core layer subsequently undergoes patterning, such as by lithography and etching processes, from which a rectangular cross-section channel is formed. An overcladding polymer film layer is then disposed on top of the waveguide core and the exposed undercladding film layer.
Various optical devices such as integrated splitters, couplers, arrayed waveguide gratings, and optical waveguide amplifiers can be formed with optical waveguides. In phase sensitive optical waveguide devices, such as directional couplers, Mach-Zender interferometers, arrayed waveguide gratings (AWG), etc., the wavelength responses of the devices vary significantly with environmental temperature changes, as shown in FIG. 1. This variance is due to the large thermal expansion coefficient and the large optic coefficient of polymer materials. Due to these large coefficients, operation of these optical waveguide devices requires temperature control, thereby increasing device complexity and manufacturing cost.
Keil et al. “Athermal all-polymer arrayed-waveguide grating multiplexer,” Electronics Letters, Vol. 37, No. 9, Apr. 26, 2001, have disclosed fluoroacrylate-type polymers such as a terpolymer of pentafluorostyrene, trifluoroethylmethacrylate, and glycidylmethacrylate disposed on a polymer substrate as AWG's. However, these fluoroacrylate-type polymers contain numerous C—H bonds. Polymers with C—H bonds typically have high absorption in the infrared region where the optical communication signals reside, at approximately 1.5 μm. This absorption causes optical communication signal loss.
Suh et al. U.S. Pat. No. 6,100,371, disclose using a polyimide polymer. However, polyimides disclosed by Matsuura et al. contain numerous C═O bonds.
Joo-Heon Ahn et al. “Polymeric 1×8 Arrayed Waveguide Grating Multiplexer using Fluorinated Poly(ether ketone) at 1550 nm,” Proceedings of SPIE, Terahertz and Gigahertz Photonics, Vol. 3795, pg. 568–575, Denver, Colo. (July 1999), disclose a waveguide grating having a silicon substrate and use synthesized polyetherketone as the core material.
It is desirable to have polymer waveguide devices that are intrinsically athermal, i.e., the wavelength responses of the devices are have reduced sensitivity to environmental temperature changes, but exhibit low absorption loss around the 1.5 μm infrared communication wavelength, as well as exhibit a reduced amount of birefringence.